1. Technical Field
One or more embodiments of the present invention relate to an electric leakage detection apparatus that detects an electric leakage of a DC power supply.
2. Related Art
A high-voltage DC power supply is mounted on an electric automobile in order to drive a motor and an in-vehicle instrument. The DC power supply is electrically insulated from a grounded vehicle body. However, when the DC power supply and the vehicle body are electrically connected for any cause, a current is passed from the DC power supply to the ground through the vehicle body to generate an electric leakage (or a ground fault). Therefore, a detection apparatus that detects the electric leakage is provided in the DC power supply. Japanese Unexamined Patent Publication No. 2003-250201 discloses a ground fault detection apparatus mounted on the electric automobile.
In the vehicle ground fault detection apparatus of Japanese Unexamined Patent Publication No. 2003-250201, a positive terminal of the DC power supply is connected onto one end side of a coupling capacitor, the coupling capacitor is charged by applying a rectangular wave pulse signal to a measuring point that constitutes the other end side of the coupling capacitor, and a voltage signal generated at the measuring point is detected to detect the ground fault of the DC power supply. A difference between a voltage measured at the measuring point at the time the rectangular wave pulse signal becomes a first phase and a voltage measured at the measuring point at the time the rectangular wave pulse signal becomes a second phase is obtained, and the ground fault of the DC power supply is detected based on the difference of the voltage.
In the vehicle ground fault detection apparatus of Japanese Unexamined Patent Publication No. 2003-250201, a cycle of the pulse supplied to the coupling capacitor is kept constant. After a charge of the coupling capacitor is completed, a discharge from the coupling capacitor is started, and it takes a predetermined time to decrease a voltage at the measuring point to 0 volts since the discharge is started. A time interval after the pulse falls until a next pulse rises is set equal to or more than the predetermined time required for the discharge. Therefore, when a determination of the presence or absence of the ground fault is made by detecting the voltage at the timing the pulse falls or rises, a time interval from the pulse fall to the pulse rise is lengthened to cause an issue in that it takes time to make a determination.
Japanese Unexamined Patent Publication No. 2008-89322 discloses an apparatus that detects an insulating state of the DC power supply based on the voltage at the capacitor. In this apparatus, a reset switch is provided in order to discharge the capacitor, the apparatus waits for the voltage between both ends of the capacitor to be decreased to a given voltage when the voltage between both the ends of the capacitor exceeds a maximum voltage during a normal operation, and the reset switch is powered on to rapidly charge the capacitor when the voltage between both the ends of the capacitor becomes the given voltage.